In the manufacturing of a semiconductor device, the device is usually processed at many work stations or processing machines. The transporting or conveying of partially finished devices, or work-in-process (WIP) parts, is an important aspect in the total manufacturing process. The conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e. as many as several hundred, is usually required to complete the fabrication process. A semiconductor wafer or IC chips must be transported between various process stations in order to perform various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, ion implantation, etching and passivation steps must be carried out before an IC chip is packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e. a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically guided vehicles (AGV) or overhead transport (OHT) vehicles that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes pods, such as SMIF (standard machine interface) or FOUP (front opening unified pod), and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rails of the conveying vehicle.
An OHT system is frequently used to deliver a cassette pod such as a FOUP to a process machine. This is shown in FIG. 1. A cassette pod 10 of the FOUP type is positioned on a loadport 12 of a process machine 14. The loadport 12 is frequently equipped with a plurality of locating pins 16 for the proper positioning of the cassette pod 10. A detailed perspective view of the FOUP 10 is shown in FIG. 2. The FOUP 10 is constructed of a body portion 18 and a cover 28. The body portion 18 is provided with a cavity 46 equipped with a plurality of ribs 48 for the positioning of 25 wafers of the 300 mm size. The body portion 18 is further provided with sloped handles 50 on both sides of the body for ease of manual transportation. On top of the body portion 18, is provided with a plate member 52 for gripping by a transport arm (not shown) of an OHT system (not shown).
When the cassette pod 10 is positioned on the process machine 14, and the cover 28 is removed to expose an opening to cavity 46, a robot arm (not shown) equipped with a wafer blade (not shown) is used to unload wafers from the cassette pod 10 and deliver the wafers to the process chamber of the process machine 14. After the wafer has been processed in the process chamber, it is again transported by the robot arm back into the cassette pod 10. The operation or the movement of the robot arm therefore must be accurately calibrated for the wafer pick-up and delivery operations. When a FOUP is used for storing 300 mm wafers, the FOUP is frequently fabricated of a non-transparent plastic material. It is therefore difficult to visually detect the movement of the robot arm, i.e and thus the wafer blade, through the housing of the FOUP.
When a robot teaching is poor during an insulation process of the process machine or after a preventive maintenance procedure has been conducted, the poor robot teaching can lead to serious processing difficulties due to the inaccurate position of the robot arm, i.e. and thus the wafer blade. For instance, when a robot arm reaches into the cavity too deeply, an edge of the wafer may rub against the interior surface of the front panel of the housing and thus causing serious particle issues. On the other hand, if the robot arm does not reach deep enough into the cavity during the placement of a wafer and thus placing a wafer inaccurately in the cavity, the edge of the wafer may collide with the FOUP door during a door closing operation. The collision of the wafer with the FOUP door may cause serious damage to the wafer, or may even cause breakage of the wafer.
As a result, the robot teaching for picking up or delivering the wafer from or to a cassette pod cavity must be accurately performed. Presently, the robot teaching is conducted by visual examination with human eyes which is frequently inaccurate due to human error or the subjectiveness of the human operator.
It is therefore an object of the present invention to provide an apparatus for robot teaching that does not have the drawbacks or the shortcomings of the conventional apparatus.
It is another object of the present invention to provide a calibration cassette pod for robot teaching that can eliminate human error and human subjectiveness.
It is a further object of the present invention to provide a calibration cassette pod for robot teaching by installing an optical detector inside the calibration cassette pod.
It is another further object of the present invention to provide a calibration cassette pod for robot teaching wherein a light emission source and a photo diode receiver are installed to detect the position of an edge portion of a wafer.
It is still another object of the present invention to provide a calibration cassette pod for robot teaching that can be used in a portable manner for calibrating a plurality of robot arms.
It is yet another object of the present invention to provide a method for calibrating a robot arm by a calibration cassette pod that does not have the drawbacks or the shortcomings of the conventional method.
It is yet another object of the present invention to provide a method for calibrating a robot arm by a calibration cassette pod wherein a robot arm is first manually operated to load a wafer into a cassette cavity correctly to reset a process controller to zero.